Decolorization of polyethylene polyamines using cobalt/copper/chromium

ABSTRACT

The present invention relates to a process for the reduction of the color of polyamines by reacting at elevated temperature, e.g. 120°-170° C., and pressure, e.g. 500 to 6000 psig. the colored polyamines, e.g. triethylenetetramine and tetraethylenepentamine, in the presence of a cobalt on alumina hydrogenation catalyst promoted with copper and chromium. In the process of the present invention, the polyamines can either be distilled into a narrow product composition and then hydrogenated, or a crude polyamine product can be hydrogenated and then distilled to produce the desired product composition.

FIELD OF THE INVENTION

The invention relates to methods for decolorizing polyamines and moreparticularly relates, in one embodiment, to methods for decolorizingpolyethylene polyamines using catalytic hydrogenation.

BACKGROUND OF THE INVENTION

In the various methods for making polyamines and mixtures thereof, oftencolor bodies are formed which give the polyamine product an undesirablehue. Several processes have been proposed or used commercially for theremoval of color bodies from mixed polyamine products. These processesencompass both physical and chemical methods.

For example, U.S. Pat. No. 4,766,247 relates to a process for thereduction of the color of polyamines by reacting at elevated temperatureand pressure the colored polyamines, e.g. triethylenetetramine (TETA) ortetraethylenepentamine (TEPA), in the presence of a hydrogenationcatalyst, e.g. Raney nickel, palladium or ruthenium on carbon, and ahydrogen atmosphere for a period of time sufficient to effectuate thedesired reduction in color. In the '247 process, the polyamines caneither be distilled into a narrow product composition and thenhydrogenated or a crude polyamine product can be hydrogenated and thendistilled to produce the desired product composition.

A process for decolorizing polyethylene polyamines, such as TETA, andhigher homologues, such as TEPA, by treatment with active carbon atelevated temperatures followed by distillation is described in U.S. Pat.No. 3,723,529.

U.S. Pat. No. 3,595,921 describes that the color content of thepolyethylene polyamine products prepared by the reaction of ethylenedichloride with ammonia is reduced by refluxing the product in thepresence of at least about 0.5 wt. % potassium hydroxide for at leastone hour at a temperature of about 110° to about 190° C. at the reducedpressure corresponding to the refluxing temperature. Polyethylenepolyamine product having a substantially reduced color content isrecovered from the refluxing mixture.

A process for decolorizing discolored polyethylene polyamines bydistilling the polyamines in the presence of polyethylene polyaminehydrochloride is described in British Patent 1,351,050. Similarly, U.S.Pat. No. 4,570,019 describes a process which may be run continuously forproducing polyethylene polyamines having improved color characteristicswhich comprises treating discolored polyethylene polyamines withpolyethylene polyamine hydrochloride in the presence of water atelevated temperatures for the time necessary to reduce the color of thepolyethylene polyamines. The decolorized polyethylene polyamines arethen flash evaporated from the treating mixture.

A process for decolorizing discolored polyethylene polyamine bycontacting the discolored polyamine with a chlorinated hydrocarbon, e.g.an alkyl chloride or an alkylene chloride, and then distilling theresultant mixture to separate the decolored polyamine is mentioned inEuropean Patent 0 150 075 B1.

Finally, U.S. Pat. No. 4,731,165 teaches a process of decoloring crudeTETA through contact with a sulfonic acid ion exchange resin. Subsequentdistillation at elevated temperature obtains decolored TETA.

Some catalytic hydrogenation decoloration techniques use catalysts withshort lifetimes. Others tend to be unduly complicated. Thus, thereremains a need for new methods to decolorize polyamines without some ofthe disadvantages of the prior methods.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod for decolorizing polyamines in the presence of hydrogen and acatalyst.

It is another object of the present invention to provide a method forcatalytic hydrogenation to decolorize polyethylene polyamines which usesa catalyst having a long life.

In carrying out these and other objects of the invention, there isprovided, in one form, a process for reducing the color of a polyamineproduct comprising contacting the product at elevated temperature andpressure with a catalytically effective amount of a cobalt on aluminahydrogenation catalyst promoted with copper and chromium in the presenceof a hydrogen-containing atmosphere.

DETAILED DESCRIPTION OF THE INVENTION

Polyethylene amines such as triethylenetetramine (TETA) andtetraethylenepentamine (TEPA) can be produced by reacting analkanolamine, an alkyleneamine and optionally either ammonia or aprimary or secondary amine in the presence of a catalytic amount of aphosphorous containing catalyst, e.g. phosphoric acid on silica-aluminaor Group IIIB metal acid phosphate. The reaction can be conducted at atemperature from about 175° to 400° C., under a pressure sufficient tomaintain a substantial amount of ammonia or amine in the reaction zoneand particularly under vapor phase conditions. The polyamine productrapidly develops a tan to brown color, i.e. 7-8 on the Gardner colorscale, ASTM Method D-1544.

Polyethylene polyamines made by reacting ethylene dichloride and ammoniaor reacting an alkyl halide and a diamine also have varied color levels.Indeed, polyethylene polyamines tend to discolor when exposed to air forextended periods, and it is usually recommended that storage vessels beequipped with nitrogen blanketing when the color of the polyamine isimportant.

Discoloration of the polyamine product produced by any method limits theapplications for the discolored TETA and TEPA. The colored products thushave limited commercial potential.

It has been discovered that the color of polyethylene poiyamines orother polyalkylene polyamines, and perhaps polyamines in general, may bereduced or eliminated by subjecting them to a mild hydrogenationprocess. Basically, the polyethylene polyamines made by any process arereacted with a hydrogen atmosphere in the presence of a cobalthydrogenation catalyst promoted with copper and chromium on an aluminasupport at elevated temperature and pressure. Without being bound by anyparticular explanation, it is believed that during the process thechromophores, i.e. color bodies, are reduced or eliminated; the exactmechanism of the process is unknown.

More specifically, the process involves contacting a colored polyamineproduct with a catalytically effective amount of a Co/Cu/Cr on aluminahydrogenation catalyst in the presence of a hydrogen-containingatmosphere at elevated temperature and pressure. For the process, thepolyamine product can be any polyalkylene polyamine. This polyamineproduct produced by any of the applicable preparation processes caneither be treated for color reduction as a crude product, i.e. asproduced from the applicable preparation process, or be distilled intoselected cuts and then treated. In one embodiment of the invention, thepolyamines have at least some compounds with the formula

    NH.sub.2 --CH.sub.2 CH.sub.2 --(NH--CH.sub.2 CH.sub.2).sub.n --NH.sub.2

where n ranges from 2 to 6. It will be appreciated that often thepolyethylene polyamine will be a mixture of amines. In one embodiment,the greatest single component in the polyamine product istriethylenetetramine; in another, the greatest single component istetraethylenepentamine.

The catalyst is Co/Cu/Cr on an alumina support. Preferably, the catalystcontains from about 30-40 wt. % cobalt, from about 7-13 wt. % copper,from about 0.1-3 wt. % chromium, with the balance aluminum. The copperand chromium serve as promoters for the cobalt. Enough catalyst shouldbe used to be effective in reducing or eliminating the color in thepolyamine product.

The process of the present invention can either be performed in a batchor continuous mode of operation utilizing either a fixed bed or slurrytype reactor. Generally, the elevated temperature should be from about120° to about 170° C., preferably from about 120° to about 160° C. Theelevated pressure ranges from about 500 psig to about 6000 psig,preferably from about 1000 to about 5000 psig. If a batch process isused, the batch times may range from about 0.1 to about 4 hours. In acontinuous process, the space velocity may range from about 0.1 g/hr-cccatalyst to about 1.0 g/hr-cc catalyst.

The invention will be further illustrated in the following Exampleswhich are not intended to limit the spirit and scope of the invention,but rather merely to more completely illuminate the invention.

Examples 1-3 Color Reduction of TEPA Polyamines

The tests were carried out in a 100 cc electrically heated stainlesssteel tubular up-flow reactor which was filled with the indicatedcatalyst (see Table I). TEPA and hydrogen were continuously fed to theheated reactor. Reactor pressure was maintained at 2500 psig with a backpressure regulator. Reactor effluent samples were analyzed by GLC andare given in Table II. Color numbers of reactor effluent samples arelisted in Table I.

Example 4 Catalyst Life Study

A catalyst life study on Co/Cu/Cr on alumina for TEPA decolorization wasalso conducted. The spent catalyst from Example 1 was charged back tothe reactor and run at the same conditions for 1000 hours. The reactoreffluents were distilled. No significant catalyst activity loss wasnoted throughout the run..After distillation, TEPA products with colorsof Pt-Co 100-125 (green hue) were obtained. The particular catalystsused in these Examples are extrudates, but the catalysts do not have tobe limited to those formed by extrusion.

                  TABLE I                                                         ______________________________________                                        TEPA Decolorization                                                                                   H.sub.2  Color                                                  Temp.,                                                                              LHSV,   LHSV     (Gardner)                                    Ex.  Catalyst   °C.                                                                            g/hr-cc                                                                             (l/hr-cc)                                                                            Feed Product                             ______________________________________                                        1    Co-Cu-Cr/  135     0.3   0.1    9     2+                                      alumina                                                                  2    G-62RS     135     0.3    0.15  9    6                                        (United)                                                                 3    Co-0164    140     0.3   0.1    9    5                                        (Engelhard)                                                              ______________________________________                                         Catalyst G62RS is 34.5% cobalt on a silicabased support; Co0164 catalyst      is 25% cobalt on a silicabased support.                                  

                  TABLE II                                                        ______________________________________                                        TEPA Compositions (wt. %)                                                     Component        Feed    Ex. 1   Ex. 2 Ex. 3                                  ______________________________________                                        Diethylenetriamine (DETA)                                                                      0.251   0.376   0.629 0.541                                  Triethylenetetramine (TETA)                                                                    1.184   1.470   1.029 1.579                                  Hydroxyethyl     1.509   1.333   1.002 1.457                                  DETA (HEDETA)                                                                 Piperazinoethylenediamine                                                                      0.187   2.351   2.692 3.697                                  (PPEDA)                                                                       Aminoethyl       10.141  9.540   9.916 9.331                                  TETA (AETETA)                                                                 Tetraethylenepentamine                                                                         66.491  63.579  63.038                                                                              61.236                                 (TEPA)                                                                        Aminoethyl       6.553   6.914   6.043 6.060                                  PPEDA (AEPEEDA)                                                               Piperazinoethyl  8.153   8.164   7.802 8.724                                  DETA (PEDETA)                                                                 Pentaethylenehexamine                                                                          1.314   1.380   1.701 1.896                                  (PEHA)                                                                        Total Others     4.217   4.896   6.148 5.479                                  ______________________________________                                    

Many modifications may be made in the process of this invention withoutdeparting from the spirit and scope thereof which are defined only inthe appended claims. For example, one skilled in the art may discoverthat particular reaction conditions, sequences, and Co-Cu-Craluminacatalysts which may not be explicitly recited herein, but which anevertheless anticipated, would give optimal or otherwise desirableresults.

We claim:
 1. A continuous process for reducing the color of a polyamineproduct comprising contacting the product at elevated temperature andpressure with a catalytically effective amount of a cobalt on aluminahydrogenation catalyst promoted with copper and chromium in the presenceof a hydrogen-containing atmosphere, where the catalyst has a lifetimein this process of at least 1,000 hours.
 2. The process of claim 1 wherethe elevated temperature is in the range of 120° to 170° C.
 3. Theprocess of claim 1 where the elevated pressure is in the range of 500 to6000 psig.
 4. The process of claim 1 where the hydrogenation catalystcontains from about 30-40 wt. % cobalt, about 7-13 wt. % copper, about0.1-3 wt. % chromium and the balance alumina.
 5. The process of claim 1where the greatest single component in the polyamine product istriethylenetetramine.
 6. The process of claim 1 where the greatestsingle component in the polyamine product is tetraethylenepentamine. 7.The process of claim 1 further comprising distilling the polyamineproduct following the contacting step to further reduce color.
 8. Acontinuous process for reducing the color of a polyamine productcomprising contacting the product at elevated temperature between 120°to 170° C. and pressure between 500 to 6000 psig with a catalyticallyeffective amount of a cobalt on alumina hydrogenation catalyst promotedwith copper and chromium in the presence of a hydrogen-containingatmosphere, where the catalyst has a lifetime in this process of atleast 1,000 hours.
 9. The process of claim 8 where the hydrogenationcatalyst contains from about 30-40 wt. % cobalt, about 7-13 wt. %copper, about 0.1-3 wt. % chromium and the balance alumina.
 10. Theprocess of claim 8 where the greatest single component in the polyamineproduct is triethylenetetramine.
 11. The process of claim 8 where thegreatest single component in the polyamine product istetraethylenepentamine.
 12. The process of claim 8 further comprisingdistilling the polyamine product following the contacting step tofurther reduce color.
 13. A continuous process for reducing the color ofa polyamine product comprising contacting the product at elevatedtemperature between 120° to 170° C. and pressure between 500 to 6000psig with a catalytically effective amount of a cobalt on aluminahydrogenation catalyst promoted with copper and chromium containing fromabout 30-40 wt. % cobalt, about 7-13 wt. % copper, about 0.1-3 wt. %chromium and the balance alumina, in the presence of ahydrogen-containing atmosphere, where the greatest single component inthe polyamine product is selected from the group consisting oftriethylenetetramine and tetraethylenepentamine, where the catalyst hasa lifetime in this process of at least 1,000 hours and where theresulting color of the polyamine product is about Gardner
 2. 14. Theprocess of claim 13 further comprising distilling the polyamine productfollowing the contacting step to further reduce color.